Method of burning molded carbon bodies in round-down-draft kilns

ABSTRACT

A process for burning molded carbon bodies in round down-draft kilns, which comprises cooling at least one of the chambers ahead of the fire box by the introduction of cold gases or vapors.

United States ?aieni 1 1 1111 3,744,959

Nedopil et a1. July 1%, 1973 [5 METHOD OF BURNING MOLDED CARBON [56] References Cited BODIES IN ROUND-DOWN-DRAFT KILNS UNITED STATES PATENTS Inventors: Erich p g g; Wilfried 2,699,931 1/1955 Buhleret ai. 263/52 Krohe, Niederhochstadt, both of 2,607,199 8/1952 Christensen 1 34/20 Germany; Karl Wittmann, Bad 2,318,576 5/1943 Arnold 34/20 X Goisern-Reitern, Austria [73] Assignee: Sigri Elektrophit GmbH, Meitingen near q g Germany Primary Exammer-John J. Camby Att0rneyCurt M. Avery, Arthur E Wilfond, Herbert {22] Filed: Feb. 18, 1971 L. Lerner and Daniel J. Tick [21] Appl. NO.: 116,534

[57} ABSTRACT {30] Foreign Application Priority Data A process for burnmg molded carbon bod1es in round 5:: 3 2 gammy g down-draft kilns, which comprises cooling at least one a many Of the chambers ahead of the fire box by the introduc- 152 vs. (:1 432/12, 34 20, 432/6 of Cold gases vapors [51] Int. Cl. F27b 13/02 [58] Field of Search 263/36, 39, 52; 10 Claims, 3 Drawing Figures 1 O 19 Q 1 ,1 f i\ 2O i9 18 i7 i6 i5 111 13 i2 H 1 v 1 1 1 1 1 1 U O O O O O O {Na 0 I r *T Patented July 10, 1973 I5; Sheets-finest i Patented July 10, 1973 15 sheetssheet Patented Juiy 1D, 1973 3,744,959

5 Sheets-Sheet 5 METHOD OF BURNING MOLDED CARBON BODIES IN ROUND-DOWN-DRAFT KILNS Our invention relates to a method of regulating the heating rate during the burning of molded carbon bodies in round down-draft kilns.

During the burning of molded carbon bodies consisting of mixtures of solid carbonaceous substances, such as e.g., cokes, graphites and soots with binders, such as coal tar asphaltum and synthetic resins, solid cokes form from said binders, together with gaseous swelling products and free hydrogen. The amount of swelling gases and hydrogen developing per unit time is a function of the heating rate, as well as the volume of the binder content. It is known that during the burning process, the specific heating rate applying for each carbon quality is not to be exceeded, if the burning is to be free of rejects. If the gas quantity is too high, tears and other structural faults will occur in the molded carbon bodies, thus reducing the value of the end product or completely eliminating industrial utilization.

Round down-draft kilns wherein formed carbon bodies are preferably burned comprises a number of chambers connected through flue or boiler gas and fresh air ducts. The flue gas is sucked in by the firing chamber to the chimney via newly charged chambers which are connected in series. The flue gas thereby relinquishes a portion ofits sensible heat, giving it up to the combustion product, so that the heating rate of the combustion product may be regulated within given limits, by the design of the furnace, through changes in the chimney draft. It is not possible, however, to differentiate the heat dissipation and to make the temperature gradient smaller in the critical coking phase between 300 and 600 C, wherein large swelling gas volumes are formed or within the range of 600 to 750 C, wherein greater amounts of hydrogen are released, than in the chambers which are connected ahead and behind. The chamber temperatures may also rise more than linearly in the critical temperature range between 300 and 600 C, due to ignition and combustion of the swelling gases (which cannot be completely avoided) with the air, contained in the flue gas.

In order to avoid burning waste, a very small temperature rise must be maintained also in the non-critical ranges, particularly in furnaces with large chamber dimensions.

Our invention has among its objects the reducing of the temperature rise in the coking chamber, between about 300 and 600 C, so that no waste results from the formation of tears in the formed carbon bodies. At the same time, the ahead of and after connected chambers are to be heated with higher temperature gradients or, in other words, chamber temperatures are to be regulated independently from their adjacent chambers.

According to the invention, one or more ofthe chambers connected ahead of the boiler or boilers, are cooled by the introduction of cold gases or vapors. Suitable for cooling purposes are all gases and vapors which do not attack the ceramic brick lining of the chambers, for example, air, nitrogen, carbon dioxide and water vapor.

The method of the invention limits the temperature rise in the chambers of round down-draft kilns within a temperature range between 350 and 600 C, so that no tears occur in formed carbon bodies. The temperature gradients in less critical ranges may be increased in order to make possible a fast, economical burning of formed carbon bodies. To improve the temperature range of round down-draft kilns still further, with chambers cooled through the introduction of cold gases or vapors, it is preferred to measure the furnace draft between the tire box and the cooled chamber so as to be able to regulate the withdrawn amount of flue gas, independent of the volume of the introduced cooling gas.

Embodiments of the invention will be disclosed with reference to the enclosed drawing, wherein:

FIG. 1 shows in plan view, an annular kiln with twenty chambers Whereinto air is introduced according to the invention, for regulating the chamber temperature;

FIG. 2 illustrates the same kiln with a device for introducing water through nozzles;

FIG. 3 shows a burning curve which constitutes the median chamber temperature.

The temperature of the charge material in the fire box 1 (FIG. 1) heated with heating oil, amounts to 1,000 C. The combustion air is sucked in through the covered chamber 17 via chambers l8, l9 and 20, to the fire box, being heated thereby, by cooling the chamber contents. The fire box gas flows in clockwise direction from the box or chamber 1 via chambers 2, 3 etc., to chamber 12 and from there through the transport line 21, into the flue gas channel which leads to the chimney. in this manner, the flue gas dissipates a large part of its sensible heat to the charge product in the chambers 2 to 12.

According to the method of the invention, air is sucked into the chamber through a brick channel which leads to the slotted flange wall of the chamber. The underpressure effected by the chimney draft in the chamber, amounts to about 10 to 15 mm Hg. Regulation of the supplied volume of air is possible through a throttle valve which engages the inlet opening of the channel. The furnace draft is measured with the manometer 25, situated at chamber 4, in order to regulate the amount of flue gas to be withdrawn.

FIG. 2 discloses another example of the method according to the invention. Four nozzles 123 directed against the opening of the fire shafts and connected with the water line 124, pass through the cover of the chamber 6. The chamber temperature is measured by thermoelement 125, which also passes through the chamber cover. As soon as the chamber temperature exceeds a critical limit determined by preliminary tests, slide valve 26 is opened and Water is sprayed into the fire shafts of the chamber 6. The water drops evaporate in the rising up current of flue gas and cool the gas down to a non-critical value. According to the invention, the valve 26 maybe controlled in a known manner, via the thermal voltage of the thermoelement 25.

To cool-the chamber around approximately 50 C, about 50 to liters of water are required, at a total volume of flue gas between 80,000 to 100,000 Nm /h. The temperature of the chamber 7, connected in series, was not changed by cooling.

The invention is not limited to the disclosed examples. More particularly, several of the chambers connected behind the boiler or boilers may be cooled through the spraying-in of water or cooled partly by water and partly by cold gases or vapors. To effect a speedy vaporization of the sprayed-in water it is preferable, especially with respect to small chamber dimensions, to introduce water through a nozzle supplemented with compressed air.

FIG. 3 shows chamber temperatures attained in accordance with the method of the invention (interrupted curve) compared to the temperature of a burning without boiler-gas cooling (drawn-out curve). By cooling the boiler gas according to the invention, the temperature rise in the critical coking range was considerably reduced, at a generally unchanged burning rate while the waste during the burning of cylindrical electrodes went down from about 5 percent to less than 1 percent.

The invention is not limited to the disclosed examples. Most particularly, any inert, non-aggressive gas, each inert vapor or vaporizable liquid may be used for cooling purposes. The feed-in of the coolant is feasible into each or even several chambers, between the fire box and the flue gas outlet. The coolant may also be sucked in, for example, through suitable openings provided in the chamber covers, into the chambers to be cooled or may be forced thereinto; to effect a better through-mixing with the boiler gases, eddy nozzles or similar devices should be provided.

The advantages of the method of the invention lie particularly in the fact that in round down-draft kilns, the burning curves may be adjusted to the characteristics of the formed carbon bodies which are to be burned, which results in shorter burning periods, accompanied by a smaller burning waste.

We claim:

1. In the process for burning carbon bodies in round down-draft kilns comprising a series of longitudinally disposed successive sections including preheating, firing and cooling zones, each section comprising a plurality of chambers adapted to contain the carbon bodies and a protective packing material. each of the chambers containing fire shafts, fluid fuel burner units disposed in at least one of the chambers of the firing zone and fans to suck flue 'gas from the firing zone through the preheating zone to a chimney, the improvement which comprises cooling at least one of the chambers of the preheating zone by the introduction of cold gases or vapors.

2. The process of claim 1, wherein a plurality of chambers are cooled in the preheating zone.

3. The process of claim 1, wherein air is used as the cooling gas.

4. The process of claim 1, wherein water vapor is used as the cooling gas.

5. The process of claim 1, wherein cooling water is sprayed into one chamber of the preheating zone.

6. The process of claim 5, wherein the cooling water is sprayed against the tire shafts in the preheating zone.

7. The process of claim 5, wherein the cooling water is sprayed with compressed air.

8. The process of claim 5, which includes measuring the temperature in the one chamber of the preheating zone and, in accordance therewith, controlling the amount of the cooling water sprayed.

9. The process of claim 1, wherein the one chamber of the preheating zone is cooled, partially by spraying water and partially by the introduction of cold gas or vapor.

10. The process of claim 1, which includes measuring the draft between the firing zone and the cooled chamber in the preheating zone. 

1. In the process for burning carbon bodies in round down-draft kilns comprising a series of longitudinally disposed successive sections including preheating, firing and cooling zones, each section comprising a plurality of chambers adapted to contain the carbon bodies and a protective packing material, each of the chambers containing fire shafts, fluid fuel burner units disposed in at least one of the chambers of the firing zone and fans to suck flue gas from the firing zone through the preheating zone to a chimney, the improvement which comprises cooling at least one of the chambers of the preheating zone by the introduction of cold gases or vapors.
 2. The process of claim 1, wherein a plurality of chambers are cooled in the preheating zone.
 3. The process of claim 1, wherein air is used as the cooling gas.
 4. The process of claim 1, wherein water vapor is used as the cooling gas.
 5. The process of claim 1, wherein cooling water is sprayed into one chamber of the preheating zone.
 6. The process of claim 5, wherein the cooling water is sprayed against the fire shafts in the preheating zone.
 7. The process of claim 5, wherein the cooling water is sprayed with compressed air.
 8. The process of claim 5, which includes measuring the temperature in the one chamber of the preheating zone and, in accordance therewith, controlling the amount of the cooling water sprayed.
 9. The process of claim 1, wherein the one chamber of the preheating zone is cooled, partially by spraying water and partially by the introduction of cold gas or vapor.
 10. The process of claim 1, which includes measuring the draft between the firing zone and the cooled chamber in the preheating zone. 